1. Field of the Invention
The present invention relates to a method of manufacturing a polyelectrolyte such that ion groups are introduced into polystyrene resin.
2. Description of Prior Art
Polystyrene resin has excellent electric characteristic, satisfactory rigidity and sufficient water resistance while exhibiting low costs. Therefore, the polystyrene resin is solely or formed into an alloy combined with a copolymer or another resin so as to be used in buffers (foamable styrol), packing materials, electric products and frames and various parts for automobiles. Thus, the polystyrene resin is a general-purpose resin considered equal to polyolefin resin represented by polyethylene.
In addition to the purpose of the polystyrene resin for use as the structural material, the polystyrene resin is refined into a polyelectrolyte so as to be used as coagulant for waste water treatment, an additive for cement, a material for fluidizing coal slurry, dispersant for inorganic pigment, a material for reinforcing paper, a surface sizing material for paper, a conductive material for an electronic copying machine, a destaticizer, a scale preventive material, dispersant for emulsion polymerization and aqueous glue and the like.
To refine the polystyrene resin into a polyelectrolyte, for example, a method may be employed in which sulfonate or an amine salt subjected to a chloromethylation process is introduced into the polystyrene resin so that the polystyrene resin is formed into a water-soluble polymer.
However, an actual process for refining the polystyrene resin into a polyelectrolyte encounters a variety of problems.
For example, sulfonation of the polystyrene resin, which is performed in a sulfonating agent, requires a large quantity of the sulfonating agent, represented by concentrated sulfuric acid. Moreover, the large quantities of the sulfonating agent and water for cleaning the sulfonating agent are discharged after the reactions have been performed. Thus, there arises a problem in that resources cannot be saved, the waste cannot be reduced and the manufacturing cost cannot be reduced. If the sulfonating operation is performed as described above, molecule crosslinking (sulfon crosslinking) easily occur when reactions are performed. Thus, the polymers are allowed to gel and therefore unnecessary polymers can easily be formed in water. Moreover, the foregoing gelation becomes apparent in proportion to the molecular weight of the polymer and the molecule chains of the polymers can easily be cut. Therefore, a high molecular polyelectrolyte cannot easily be obtained.
When the sulfonating reactions are performed in a chlorine solvent, a large quantity of the chlorine solvent remains in the polyelectrolyte after subjected to the reactions and its water solution. As a result, halogen compounds are contained in the polyelectrolyte product. Therefore, if the foregoing polyelectrolyte is used in the coagulant for waste water treatment, dispersant for cement, absorbing resin, a surface sizing material for paper or the like, the halogen compounds are discharged into waste water. Thus, the foregoing polyelectrolyte cannot practically be employed because of difficulty to satisfy a waste water regulation.
Since the molecular weight (Mw) of the thus obtained polyelectrolyte is generally 150,000 to 600,000, a polyelectrolyte having a large molecular weight has been required to improve the performance when the polyelectrolyte is used as, for example, a coagulant.
Since the sulfonating reaction encounters reduction in the reaction rate if water is contained in the system, water must completely be removed to again use the solvent in the reactions.
However, a conventional technique, for example, still standing separation, involves a fact that sulfonated substances of aromatic polymers, which are reaction products, serve as surface active agents. Thus, the boundary between the aqueous layer and the solvent layer becomes confused, thus causing the separation to be made difficult. When the solvent is recovered by distillation, the solvent of the chlorine type hydrocarbon and water form azeotropic mixture. Complete removal of water from the solvent cannot easily be realized, thus causing a necessity for performing refining and dehydration processes to arise.
Therefore, there arises problems in that the working efficiency deteriorates and new additional facility is required.
What is worse, the polystyrene resin has a problem of a halogen flame retardant.
Since the halogen flame retardant has a significant flame retardant effect with respect to a variety of plastic materials and its cost is very low, the halogen flame retardant is used widely over the world.
However, use of the halogen flame retardant raises a problem because the halogen flame retardant generates halogenated hydrogen when it burns. In particular, use of decabromodiphenyl oxide (DBDPO), which is used most widely and which generates toxic substances, such as dioxine, has been regulated.
The halogen flame retardant, having excellent flame retardant effect with respect to aromatic resins represented by styrene resin, are widely used in the frames of home electronic products and as a material of parts.
Therefore, if the home electronic products are dumped, a large quantity of plastic substances containing the halogen flame retardant are discharged.
The plastic wastes are usually burnt or reclaimed except for a small portion which is recycled by heating and melting.
When the plastic wastes are attempted to be disposed by burning, the above-mentioned problem of generation of toxic gases arises. Therefore, the disposal must be performed by the reclamation at present.
The amount of plastic wastes containing the halogen flame retardant has been enlarged year by year. Therefore, the reclamation disposal is ineffective and thus there arises a critical problem for Japan considerably wanting of reclamation plants.
If recycling of plastic wastes is attempted, recycle of the plastic containing the halogen flame retardant, the use of which is regulated, is not preferable.
An object of the present invention is to provide a method of manufacturing a polyelectrolyte capable of manufacturing a polyelectrolyte containing no halogen compound while preventing discharge of a large quantity of toxic wastes.
Another object of the present invention is to provide a method of manufacturing a water-soluble polyelectrolyte having larger molecular weight.
An object of the present invention is to enable a solvent used in a sulfonating reaction of aromatic polymers to be recovered in a state where no water is contained and to form an efficient sulfonating system by recycling the solvent.
Another object of the present invention is to provide a processing method capable of efficiently separating halogen flame retardant containing plastic waste or the like.
According to one aspect of the present invention, there is provided a method of manufacturing a polyelectrolyte comprising the step of sulfonating polystyrene resin in a state where the polystyrene resin is dissolved or dispersed in a solvent composed of an alicyclic compound.
When the alicyclic compound is employed as the solvent in the process for sulfonating the polystyrene resin, gelation can be prevented. Since the necessity of using a halogen compound as the solvent can be removed, a polyelectrolyte containing no halogen compound can be manufactured without discharge of a large quantity of toxic wastes.
According to a second aspect of the present invention, there is provided a method of manufacturing a polyelectrolyte comprising the steps of introducing ion groups into copolymers of styrene and conjugate diene; and crosslinking and/or polymerizing the conjugate diene in the copolymer so that refining to a water-soluble polyelectrolyte is performed.
When the conjugate diene is previously contained in the polystyrene resin and the conjugate diene units are crosslinked and/or polymerized, the water-soluble polyelectrolyte having a large molecular weight can be obtained.
A third aspect of the present invention is characterized in that aromatic polymers are added to and dissolved in solvent supplied continuously; sulfonating agents are supplied to the solution to perform sulfonating reactions; generated reaction products and the solvents are separated from each other; and the separated solvents are returned so as to be again used in the sulfonating reactions.
In the above-mentioned aspect, the sulfonated aromatic polymers are formed into solid matters so as to be separated from the solvents. Therefore, the necessity of adding water to the reaction system can be removed.
Therefore, the separated solvents do not contain water and thus the solvents can be recycled.
A fourth aspect of the present invention is characterized in that plastics containing halogen flame retardants are subjected to an acid process in an organic solvent; ion groups are introduced into resin components to form water-soluble polymer; and then the halogen flame retardants in the organic solvent are separated.
When the plastics containing the halogen flame retardants are subjected to the acid process in the organic solvents, the ion groups are introduced into the resin components so as to be formed into water-soluble polymers so that the phase is shifted to an aqueous phase.
On the other hand, the above-mentioned introduction of the ion groups does not take place in the halogen flame retardants. Thus, the halogen flame retardants are, in the non-reacted state, retained to be the organic solvent phase.
Therefore, separation of the aqueous phase and the organic solvent phase from each other causes the resin components and the halogen flame retardants to quickly be separated from each other.
Other objects, features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.